This invention pertains to vinyl ester compounds and their use as coatings for substrates. More particularly, this invention pertains to the process for preparing such compositions derived from epoxy compounds.
It is known that many vinyl ester resins are polymerizable by radiation inducement as is illustrated in U.S. Pat. Nos. 3,560,237 (Re. 27,656); 3,661,576; 3,673,140 and British Pat. No. 1,375,177. In addition, U.S. Pat. Nos. 3,560,237 (Re. 27,656) and 3,661,576 pertain to vinyl ester resins derived from resinous epoxide compounds (i.e., epoxy resins). Many of these vinyl ester resins which are derived from resinous epoxides are commercially available, possess excellent physical and chemical properties, and are particularly useful as protective coatings for a variety of substrates. In such a utility, the vinyl ester resins are normally dissolved in an organic solvent or a reactive diluent, applied to a substrate by any one of several conventional techniques such as spraying or dipping, and cured with actinic radiation.
It is also known that certain sulfonium salts can be used as accelerators for the photopolymerization of acid polymerizable and/or acid-curable materials including epoxy resins per se, as taught in Netherland Patent Application No. 75.10320. It is taught that the sulfonium salts must be soluble in the resinous component and that the ability of a sulfonium salt to accelerate the cure of any particular material depends upon the ability of the corresponding acid, that is, the acid containing the same anion as the sulfonium salt, to cure that material. These photocurable compositions are dissolved in an organic solvent and applied to various substrates by conventional techniques.
The necessity of using an organic solvent is a commercial impediment for using the photocurable compositions set forth above. Organic solvents must be recovered and recycled or disposed of for safety, environmental or economic reasons. The recovery in many instances is difficult and costly. These problems can be reduced if the organic solvent reacts into the coating. Considerable research has been directed toward the use of vinyl monomers and low viscosity vinyl resins as reactive diluents. However, many of the useful reactive diluents, such as 2-hydroxyethyl acrylate, are toxic and represent considerable health and environmental problems.
Presently available radiation-curable systems use a reactive diluent such as an acrylic monomer to reduce the viscosity to the level required for application. Many of these diluents suffer from excessive toxicity, volatility or odor. In addition, because the diluent is incorporated into the final product, the amount and kind of diluent will affect the properties of the end coating. With conventional solvent systems, additional solvent can be added to adjust viscosity without materially affecting the properties of the final coating. However, the presence of these solvents poses a toxicity problem.
The commercial problems enumerated above have caused many potential customers to use alternate systems having different mechanisms of cure and/or different polymer structure, such as, for example, latexes. In addition, many resinous systems have been rendered water-soluble or water-dispersible by attaching various onium groups, such as sulfonium, phosphonium, or ammonium, to the backbone of the resin or by adding an onium surfactant to the resin as a dispersing vehicle. Many of these onium compounds are electroreducible, particularly the sulfonium and isothiuronium compounds, and have been used in cathodic electrodeposition processes. An exhaustive documentation of this is not required; however, reference is made to U.S. Pat. Nos. 3,793,278; 3,936,405; 3,937,679; 3,959,106 and 3,894,922 which represent a series of cases in which certain onium-modified epoxy resins are alleged to be useful as electrodepositable compositions. The onium-modified epoxy resins are typically prepared by reacting an epoxy resin with a tertiary phosphine, tertiary amine or sulfide in the presence of an acid. The acids so used typically have dissociation constants greater than 1.times.10.sup.-5, and include both organic and inorganic acids.
Harris et al. in U.S. Pat. No. 4,020,030 disclose the preparation of water-soluble or water-dispersible (oil-in-water) sulfonium-modified epoxy resins having superior coating properties and low toxicity by using epoxy resins having an epoxy equivalent weight greater than about 500 and/or by converting greater than about 70 percent of the epoxy groups in the epoxy resins by reaction with a sulfide and an acid. These sulfonium-modified epoxy resins are used as coatings on various substrates and are applied by conventional techniques as opposed to electrodeposition.
In view of the deficiencies of the conventional vinyl ester resins, it is highly desirable to provide a process for preparing sulfonium-stabilized, water-compatible ionizing radiation and light-curable vinyl ester resins in an environment that is essentially free of organic solvent.